1. Field of the Invention
The present invention relates to an electrically stimulated catalytic converter apparatus for treating engine exhaust from an internal combustion engine of a vehicle, to reduce pollutants which may be present therein. More particularly, the present invention relates to an electrically simulated catalytic converter employing a high-voltage electrical corona for treating engine exhaust, where the corona may be used either with or without a conventional ceramic monolith-type converter-type converter which is reduced in size.
2. Description of the Background Art
In motor vehicle exhaust systems, catalytic converters are widely used to reduce unwanted emissions from internal combustion engines. Catalytic converters are also used on many engine-equipped machines including generator sets, forklifts, mining equipment, trucks, buses, trains, etc., to treat the engine exhaust from engines of these machines to reduce pollutants in the exhaust.
A catalytic converter provides an environment for supporting a chemical reaction, wherein unwanted gaseous combustion by-products from an internal combustion engine are converted to more inert gases, which are generally discharged into the atmosphere outside the vehicle. A catalytic converter promotes the conversion of unwanted exhaust gases through a dense honeycomb coated with precious metals such as platinum, palladium and/or rhodium. In the conventional catalytic converter, gases such as nitrous oxides, carbon monoxide and unburned hydrocarbons are converted into reaction products such as nitrogen gas, carbon dioxide, water, etc.
However, when engine exhaust contains excessive amount of unwanted contaminants including high levels of nitrous oxides, carbon monoxide and unburned hydrocarbons, conventional catalytic converters may not be able to effectively treat/convert such excessive amount of unwanted contaminants to a safer, desired level. In such cases, it may be desired to pre-treat the engine exhaust prior to its passage through the conventional catalytic converter, and/or post-treat the engine exhaust after it is discharged from the catalytic converter, to reduce the volume of pollutants present in the engine exhaust to a safer, acceptable level.
For example, a plasma assisted catalytic reduction system—which is discussed in prior art in an online article entitled, “The Internal Combustion Engine at Work”, hereafter referred as ‘Westbrook’ apparatus—has been proposed to reduce exhaust pollution from a diesel engine prior to the exhaust entering a conventional catalytic converter (see, for example, the article at http:/www.llnl.gov/str/Westbrook.html).
FIG. 1 shows a schematic view of the Westbrook apparatus—the plasma assisted catalytic reduction system 1 having a metal wire electrode 2 placed longitudinally within the center of a cylindrical metal exhaust pipe 3, upstream of a conventional catalytic converter 4. In this known system, a non-thermal plasma is produced inside the exhaust pipe 3 by a short pulse of high-voltage applied to the wire electrode 2. According to the Westbrook article referred to above, the non-thermal plasma produced by the electrode 2 oxidizes nitric oxide and hydrocarbons to nitrogen dioxide and partially oxidized hydrocarbons, and subsequently, the conventional catalytic converter converts the nitrogen dioxide and hydrocarbons to nitrogen, carbon dioxide and water.
FIG. 2 shows the results of spectrographic analysis of exhaust emissions treated with the Westbrook apparatus, demonstrating the benefits of plasma-assisted catalytic reduction. Westbrook asserts that plasma plus catalysis almost completely eliminates unwanted exhaust emissions from diesel engines.
The charging technique by employing the Westbrook apparatus as discussed above is an intrusive technique, i.e., the wire electrode 2 is disposed within a main flow path of the engine exhaust, in a configuration substantially parallel to exhaust flow. Since the wire electrode 2 of Westbrook is not recessed away from the main flow path of the engine exhaust, the wire electrode 2 may be subjected to contamination from engine exhaust, and contaminants could build up on the single wire electrode 2 due its direct exposure to the engine exhaust. Therefore, such a single-wire corona charger may not be optimally effective, over the long term, in reducing contaminants from the engine exhaust.
Further, corona charge around a single wire electrode placed longitudinally within the exhaust conduit may not cover entire the cross-sectional area of a main flow path defined within the exhaust conduit. As a result, the entire flow of the engine exhaust may not interact with and/or pass through the corona charge, which may render such configuration of the corona charger ineffective for its intended purpose of reducing contaminants from the engine exhaust.
Also, intrusive devices such as Westbrook apparatus, as discussed above, may require cumbersome and time-consuming procedures for mounting thereof within the exhaust conduit.
The plasma-assisted catalytic reduction system requires application of a conventional catalytic converter in conjunction with a single-wire corona generator, and therefore, the Westbrook apparatus may not effective without application of a conventional catalytic converter to reduce the unwanted components present in the engine exhaust. The plasma assisted catalytic reduction system employing only a single wire electrode may not be used as a stand alone unit to treat the engine exhaust to reduce unwanted components thereof.
One example of an electrostatic charging apparatus, used in the context of air filtration, is described in U.S. Pat. No. 4,853,005 to Jaisinghani et al. In addition, several combinations of electrostatic charging apparatus employing corona chargers for various applications including treatment/purification of biological substances, waste water, combustible fluid, etc., are discussed in U.S. Pat. Nos. 5,118,942 issued to Hamade on Jun. 2, 1992; 5,077,468 issued to Hamade on Dec. 31, 1991; and 5,012,094 issued to Hamade on Apr. 30, 1991; and the disclosures of each of these three prior patents to Hamade are incorporated entirely by reference herein.
Although the known devices are usable for their intended purposes, a need still exists in the art for a corona charger device which is usable for treating engine exhaust to reduce unwanted components thereof. In particular, there is a need for an electrically simulated catalytic converter apparatus which will overcome difficulties and shortcomings encountered with the known art.